Autism Spectrum Disorders (ASD) have a devastating impact on the individual, family, and society. As many as 1 in 166 receive a diagnosis of ASD, which is characterized by disturbances in social function, communication and rigidity/repetitive behaviors. In addition, the disorder is associated with other impairing symptoms, notably obsessions and compulsions. Obsessive-compulsive disorder (OCD) is diagnosed in 37 percent of the ASD population and further limits functioning. Recent studies have identified functional abnormalities of the default network i.e. a set of brain regions activated during passive task states, and whose activity and function has been mentioned to play an important role in the development of several neuropsychiatric disorders. In addition, recent studies of ASD have shown that the disorder may be largely characterized by deficits in cognitive processes under the control of default mode structures (i.e., known to modulate social, emotional, self-relevant tasks) we hypothesized that this might be due to dysfunction of the default network. Our own preliminary data argue that obsessions and compulsions in ASD are associated with overall increased neural integrity between structures of the default network. The study proposed here aims to better understand this brain-behavior relationship. To date, no published study has documented the link between brain function in regions associated with the default network to the specific symptoms associated with obsessions and compulsions in ASD. The current study aims to address this gap in the literature. Since ASD and obsessive-compulsive symptoms can be conceptualized as disturbances in neural networks, we propose using two complementary techniques to characterize the integrity of cortical networks: resting-state functional connectivity and diffusion tensor imaging. PUBLIC HEALTH RELEVANCE: From a public health perspective, it is imperative to learn more about the neural systems underlying obsessiveness and compulsiveness in ASD, given the high prevalence of these symptoms ASD patients. This knowledge may suggest new therapeutic routes and diagnostic techniques to help treat obsessive and compulsive symptoms in ASD.